Maj. Joe Nolan is the head of a South Pacific expedition to retrieve an atomic-powered rocket that has vanished without a trace. His fellow serviceman and pilot, Lt. Danny Wilson, is also an expedition member. Aircraft mechanic Sgt. William Tatlow has also been recruited. The expedition includes the three scientists who helped build the rocket.
Their transport aircraft mysteriously crash-lands on a remote, unknown tropical island in the area where the rocket was lost on radar. Only two occupants are left on the island, a native woman and her young brother. The woman indicates something fell from the sky atop the forbidding, cloud-shrouded plateau that dominates part of the island. The rocket's fiery arrival caused the rest of the native population to abandon the island.
Expedition member Stanley Briggs dies accidentally on the steep ascent up the escarpment. After long stretches of rock climbing, the expedition emerges from what turns out to be a toxic gas cloud cover. They discover a lush, prehistoric jungle inhabited by various dinosaurs and a large field of uranium, which is what has disabled their electronic tracking equipment.
They comes upon a brontosaurus, which attacks Robert Phillips as he retreats up a tree. Nolan and Wilson open fire, but they quickly discover that the dinosaur's thick hide absorbs bullets with little effect. Later that night they set up camp. When Nolan awakes, he finds Phillips and Russian scientist Michael Rostov gone. Phillips has gotten himself stuck in a large rock crevice near a triceratops. Nolan accuses Rostov of arranging the accident on purpose, but Rostov insists that he was helping Phillips. The triceratops nearly attacks the group, but another makes a challenge and the two dinosaurs fight to the death.
Nolan is convinced that Rostov, the scientist who helped make the rocket, is up to no good because he also appeared to be able to save Stanley Briggs on their climb up but failed to do so. Eventually, Rostov reveals himself to be a victim of the Holocaust in which he lost his wife and unborn child.
Wilson later shoots a pterosaur for food near the rocket's landing site. The group soon discover the rocket is surrounded by a brontosaurus and a pair of triceratops, but Nolan devises a strategy that results in scaring off the dinosaurs with their weapons. Rostov and Phillips retrieve the needed data from the rocket. His back turned, Tatlow is gored to death by an angry triceratops, just as it is shot by Nolan and Wilson. After the team finishes a grave, violent earthquake tremors begin, and the team makes a hasty retreat down the plateau.
The four members manage to successfully return to the island's flatland, just in time to escape the island using a native outrigger canoe. The survivors watch from a distance as the island is first rocked by more violent earthquakes and then a catastrophic eruption of the island's formerly dormant volcano begins, which destroys everything.
- Cesar Romero
- Chick Chandler
- Hugh Beaumont
- John Hoyt
- Sid Melton
- Whit Bissell
- Hillary Brooke
- Shot in eleven days.
- Some sequences were tinted green on the original release prints. This was not reproduced for television prints of the film (the sequences were shown in black-and-white instead), and it was not until well over 30 years after the film's initial release that the tint was restored for home video in the late 1980s.
- Some of this film is comprised of clips from Rocketship X-M and The Terror of Tiny Town (the latter also directed by Sam Newfield).